The disposal of rubbish (trash, garbage), and other waste materials, is a problem that has concerned mankind for centuries, and that worsens with each year as populations and the sheer amount of waste increase. It has long been the practice to transport all rubbish to, and dump it at, some central site, and at the present time there are, adjacent most large towns, such dumps--or "tips"--specially designated for this purpose.
In earlier years a tip was merely an open area of ground onto which waste could be deposited, or at the very most a natural depression that could be filled up with the refuse. Later, though, much use was made of artificial pits such as result from the excavation of sand, gravel, clay, and other natural raw materials, while these days it is often necessary to construct a pit specifically for the purpose. And as dumps evolve, so the rules and regulations governing their use become more strict and more complex, in an effort to prevent their causing more problems than they solve. Specifically, it has become a regulatory requirement that every refuse pit be so constructed that none of its contents--and none of any materials that might arise from its contents--can in any way affect the ambient conditions. In particular, every pit must be so lined that nothing can seep down, into the underlying ground, and so pollute the surroundings--and especially the local water table and supply. Moreover, once the pit is full, and before earth can be laid on top and the whole landscaped, it is necessary to seal off the top as well.
A modern pit, which can vary in size from 25,000 sq.m (2.5 hectares, or about 6.25 acre) for a small pit up to 80,000 sq.m (8 ha, or about 20 acre) and beyond for a larger one--the latter are usually made up of a number of smaller pits, or "cells"--must be constructed to a set of very tight rules, and so far as leakage or seepage are concerned these relate to how the pit is lined.
Without going into too much detail, an earth pit must first have a compacted surface on top of which is a compacted sand layer with a flat and smooth surface (with no projections or indentations more that an inch--25 mm--high or deep). Then, on top of the sand, there must be laid an impervious lining layer--such as that known as a geosynthetic clay liner, or GCL. Such a liner is, in essence, a sandwich of bentonite clay between two layers of heavy-duty synthetic resin fabric (which may be either in film or in woven form). Typical examples of such liners are those made by Colloid Environmental Technologies Co. (CETCO), of Illinois, and available under the registered trademarks BENTOMAT and CLAYMAX, which cost around $5.00 per square meter. They come in rolls, each of which is a ribbon-like sheet of material (known, when deployed, as a "panel") from 3.5-5 m (12-16.5 ft) wide, from 40-45 m (135-150 ft) long, and about 10-11 mm (0.4-0.45 in) thick, and weighs, depending on the material, anywhere from 1000-1450 kg (about 2,200-3,200 lb, or about a ton to a ton and a half). These are laid directly onto the ground formation surface with an overlap--normally of around 15-22.5 mm (6-9 in), but in any case as required by the local authorities. Ignoring the overlap, it can be seen that the cost in materials alone of lining a large pit will be over $400,000.00, with another $400,000.00 or so for subsequently capping it--sealing it off once it's full. Getting the overlap right so that it is large enough to form a satisfactory seal but not so large as to waste significant amounts of material can save quite a lot of money.
The laying is commonly accomplished by the simple but effective means of threading the roll onto a support rod, attaching the rod by chains at each end to a rigid beam, mounting the beam (again with chains) to the bucket of a JCB--or a tracked 360 excavator, which is preferred if the ground is not to be churned up--and then carrying the roll along, letting the sheet liner pay out.
Unfortunately this method, though uncomplicated, is not especially accurate. Under windy conditions the unrolling liner can billow back and forth. Additionally, the chains that support the roll on the beam, and the beam on the bucket, allow the roll to swing from side to side, and it is all too easy to lay the liner such that the overlap is either too large or too small (so that there may even be a gap). Moreover, unless the roll is somehow braked, it can easily spin off excess material to form a heap.